Abstract
Reverse phase chromatography of the globin chains of adult, newborn, and fetal erythrocytes from three species of New World monkeys (Cebus apella, Aotus azarae, and Callithrix jacchus) representing three of the seven platyrrhine clades showed that gamma-globin expression was fetal in these animals. The globins were identified by a combination of chemical sequencing and mass spectrometric analysis. Since gamma-globin expression is fetal in the other major simian branch, the catarrhines, but embryonic in prosimian primates and nonprimate placental mammals, the evolution of fetal recruitment can now be assigned to the period between the simian-prosimian divergence (55 million years ago) and the platyrrhine-catarrhine divergence (35 million years ago). The gamma-globin gene underwent tandem duplication during the same evolutionary epoch, in accord with a model that suggests that the downstream duplicated gamma-gene (gamma2) was free to acquire the mutations necessary for fetal recruitment. Mass spectrometric analysis of tryptic digests of the gamma-globins verified the amino acid sequences deduced from genomic sequencing. Detailed analysis of high performance liquid chromatography and matrix-assisted laser desorption/ionization mass spectrometry data showed that gamma2-globin in Cebus was expressed to a far greater extent than gamma1-globin, supporting inferences drawn from a study of the promoter sequences. A "pre-gamma"-globin was observed in C. apella and shown to be primarily the glutathionyl adduct. The other species, A. azarae and C. jacchus, also express only one gamma-globin polypeptide. This work provides biochemical evidence of an evolutionary trend in the platyrrhines to alter the duplicated gamma-globin gene locus so that only one gamma-globin polypeptide is expressed.
Highlights
Reverse phase chromatography of the globin chains of adult, newborn, and fetal erythrocytes from three species of New World monkeys (Cebus apella, Aotus azarae, and Callithrix jacchus) representing three of the seven platyrrhine clades showed that ␥-globin expression was fetal in these animals
The data presented here, combining HPLC and mass spectroscopic analysis, establish that ␥-globin expression occurs in fetal life in platyrrhines, the New World monkeys
Because ␥-globin expression is embryonic in prosimians [2], the appearance of fetal expression occurred after the prosimiansimian divergence (55 million years ago)
Summary
Reverse phase chromatography of the globin chains of adult, newborn, and fetal erythrocytes from three species of New World monkeys (Cebus apella, Aotus azarae, and Callithrix jacchus) representing three of the seven platyrrhine clades showed that ␥-globin expression was fetal in these animals. In humans [1], the ⑀-globin gene is embryonic, expressed during the first 20% of gestation, after which it is down-regulated. A detailed comparison of differences near these conserved regions in genes that are expressed either embryonically or fetally has identified base changes associated with alternative developmental timing [5]. Studies of humans and other catarrhine primates have shown that ␥-globin expression is fetal in these species, but little data are available for the other major simian group, the platyrrhines (New World monkeys). Together with the earlier studies of catarrhine globin gene expression, these results place the emergence of fetal recruitment in the same 55–35 million years ago time period as the duplication of the ␥-globin gene [7].
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